1. Technical Field
The present invention relates to a method and apparatus for rapidly making, screening, and characterizing an array of materials in which process conditions are controlled and monitored.
2. Discussion
In combinatorial chemistry, a large number of candidate materials are created from a relatively small set of precursors and subsequently evaluated for suitability for a particular application. As currently practiced, combinatorial chemistry permits scientists to systematically explore the influence of structural variations in candidates by dramatically accelerating the rates at which they are created and evaluated. Compared to traditional discovery methods, combinatorial methods sharply reduce the costs associated with preparing and screening each candidate.
Combinatorial chemistry has revolutionized the process of drug discovery. See, for example, 29 Acc. Chem. Res. 1-170 (1996); 97 Chem. Rev. 349-509 (1997); S. Borman, Chem. Eng. News 43-62 (Feb. 24, 1997); A. M. Thayer, Chem. Eng. News 57-64 (Feb. 12, 1996); N. Terret, 1 Drug Discovery Today 402 (1996)). One can view drug discovery as a two-step process: acquiring candidate compounds through laboratory synthesis or through natural products collection, followed by evaluation or screening for efficacy. Pharmaceutical researchers have long used high-throughput screening (HTS) protocols to rapidly evaluate the therapeutic value of natural products and libraries of compounds synthesized and cataloged over many years. However, compared to HTS protocols, chemical synthesis has historically been a slow, arduous process. With the advent of combinatorial methods, scientists can now create large libraries of organic molecules at a pace on par with HTS protocols.
Recently, combinatorial approaches have been used for discovery programs unrelated to drugs. For example, some researchers have recognized that combinatorial strategies also offer promise for the discovery of inorganic compounds such as high-temperature superconductors, magnetoresistive materials, luminescent materials, and catalytic materials. See, for example, co-pending U.S. patent application No. 08/327,513 xe2x80x9cThe Combinatorial Synthesis of Novel Materialsxe2x80x9d (published as WO 96/11878) and co-pending U.S. patent application No. 08/898,715 xe2x80x9cCombinatorial Synthesis and Analysis of Organometallic Compounds and Catalystsxe2x80x9d (published as WO 98/03251), which are both herein incorporated by reference.
Because of its success in eliminating the synthesis bottleneck in drug discovery, many researchers have come to narrowly view combinatorial methods as tools for creating structural diversity. Few researchers have emphasized that, during synthesis, variations in temperature, pressure, ionic strength, and other process conditions can strongly influence the properties of library members. For instance, reaction conditions are particularly important in formulation chemistry, where one combines a set of components under different reaction conditions or concentrations to determine their influence on product properties.
Moreover, because the performance criteria in materials science is often different than in pharmaceutical research, many workers have failed to realize that process variables often can be used to distinguish among library members both during and after synthesis. For example, the viscosity of reaction mixtures can be used to distinguish library members based on their ability to catalyze a solution-phase polymerizationxe2x80x94at constant polymer concentration, the higher the viscosity of the solution, the greater the molecular weight of the polymer formed. Furthermore, total heat liberated and/or peak temperature observed during an exothermic reaction can be used to rank catalysts.
Therefore, a need exists for an apparatus to prepare and screen combinatorial libraries in which one can monitor and control process conditions during synthesis and screening.
In accordance with one aspect of the present invention, there is provided an apparatus for parallel processing of reaction mixtures. The apparatus includes vessels for containing the reaction mixtures, a stirring system, and a temperature control system that is adapted to maintain individual vessels or groups of vessels at different temperatures. The apparatus may consist of a monolithic reactor block, which contains the vessels, or an assemblage of reactor block modules. A robotic material handling system can be used to automatically load the vessels with starting materials. In addition to heating or cooling individual vessels, the entire reactor block can be maintained at a nearly uniform temperature by circulating a temperature-controlled thermal fluid through channels formed in the reactor block. The stirring system generally includes stirring membersxe2x80x94blades, bars, and the likexe2x80x94placed in each of the vessels, and a mechanical or magnetic drive mechanism. Torque and rotation rate can be controlled and monitored through strain gages, phase lag measurements, and speed sensors.
The apparatus may optionally include a system for evaluating material properties of the reaction mixtures. The system includes mechanical oscillators located within the vessels. When stimulated with a variable-frequency signal, the mechanical oscillators generate response signals that depend on properties of the reaction mixture. Through calibration, mechanical oscillators can be used to monitor molecular weight, specific gravity, elasticity, dielectric constant, conductivity, and other material properties of the reaction mixtures.
In accordance with a second aspect of the present invention, there is provided an apparatus for monitoring rates of production or consumption of a gas-phase component of a reaction mixture. The apparatus generally comprises a closed vessel for containing the reaction mixture, a stirring system, a temperature control system and a pressure control system. The pressure control system includes a pressure sensor that communicates with the vessel, as well as a valve that provides venting of a gaseous product from the vessel. In addition, in cases where a gas-phase reactant is consumed during reaction, the valve provides access to a source of the reactant. Pressure monitoring of the vessel, coupled with venting of product or filling with reactant allows the investigator to determine rates of production or consumption, respectively.
In accordance with a third aspect of the present invention, there is provided an apparatus for monitoring rates of consumption of a gas-phase reactant. The apparatus generally comprises a closed vessel for containing the reaction mixture, a stirring system, a temperature control system and a pressure control system. The pressure control system includes a pressure sensor that communicates with the vessel, as well as a flow sensor that monitors the flow rate of reactant entering the vessel. Rates of consumption of the reactant can be determined from the reactant flow rate and filling time.
In accordance with a fourth aspect of the present invention, there is provided a method of making and characterizing a plurality of materials. The method includes the steps of providing vessels with starting materials to form reaction mixtures, confining the reaction mixtures in the vessels to allow reaction to occur, and stirring the reaction mixtures for at least a portion of the confining step. The method further includes the step of evaluating the reaction mixtures by tracking at least one characteristic of the reaction mixtures for at least a portion of the confining step. Various characteristics or properties can be monitored during the evaluating step, including temperature, rate of heat transfer, conversion of starting materials, rate of conversion, torque at a given stirring rate, stall frequency, viscosity, molecular weight, specific gravity, elasticity, dielectric constant, and conductivity.
In accordance with a fifth aspect of the present invention, there is provided a method of monitoring the rate of consumption of a gas-phase reactant. The method comprises the steps of providing a vessel with starting materials to form the reaction mixture, confining the reaction mixtures in the vessel to allow reaction to occur, and stirring the reaction mixture for at least a portion of the confining step. The method further includes filling the vessel with the gas-phase reactant until gas pressure in the vessel exceeds an upper-pressure limit, PH, and allowing gas pressure in the vessel to decay below a lower-pressure limit, PL. Gas pressure in the vessel is monitored and recorded during the addition and consumption of the reactant. This process is repeated at least once, and rates of consumption of the gas-phase reactant in the reaction mixture are determined from the pressure versus time record.
In accordance with a sixth aspect of the present invention, there is provided a method of monitoring the rate of production of a gas-phase product. The method comprises the steps of providing a vessel with starting materials to form the reaction mixture, confining the reaction mixtures in the vessel to allow reaction to occur, and stirring the reaction mixture for at least a portion of the confining step. The method also comprises the steps of allowing gas pressure in the vessel to rise above an upper-pressure limit, PH, and venting the vessel until gas pressure in the vessel falls below a lower-pressure limit, PL. The gas pressure in the vessel is monitored and recorded during the production of the gas-phase component and subsequent venting of the vessel. The process is repeated at least once, so rates of production of the gas-phase product can be calculated from the pressure versus time record.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.